Polymeric interlayers and multiple layer panels made therefrom exhibiting enhanced properties and performance

ABSTRACT

Multiple layer panels including a pair of substrates and an interlayer disposed therebetween are provided. In some cases, the multiple layer panels may utilize substrates having different thicknesses, and such configurations may help reduce glass thickness and overall panel weight. However, panels of the present invention may still exhibit sufficient strength, rigidity, and acoustic performance and can be suitable for use in a wide range of automotive, aeronautical, and/or architectural applications.

BACKGROUND

1. Field of the Invention

This disclosure relates to multiple layer panels comprising polymericsheets and, in particular, to multiple layer panels comprising polymericsheets suitable for use as single or multiple layer interlayers.

2. Description of Related Art

Poly(vinyl butyral) (PVB) is often used in the manufacture of polymersheets that can be used as interlayers in multiple layer panels formedby sandwiching the interlayer between two sheets of glass. Suchlaminated multiple layer panels are commonly referred to as “safetyglass” and have use in both architectural and automotive applications.One of the primary functions of the interlayer in a safety glass panelis to absorb energy resulting from impact to the panel without allowingpenetration of an object through the glass. The interlayer also helpskeep the glass bonded when the applied force is sufficient to break theglass in order to prevent the glass from forming sharp pieces andscattering. Additionally, the interlayer can also provide the laminatedpanel with a higher sound insulation rating, reduce ultraviolet (UV)and/or infrared (IR) light transmission through the panel, and enhanceits aesthetic appeal through the addition of color, textures, etc.

Traditionally, glass panels used in automotive applications employ twoglass sheets each having a thickness between 2.0 and 2.3 mm. Most often,these sheets have approximately the same thickness. This type ofconfiguration facilitates both strength and rigidity in the final panel,which, in turn, contributes to the overall mechanical strength andrigidity of the vehicle body. Some estimates attribute up to 30 percentof the overall rigidity of a vehicle to its glass. Thus, the design andrigidity of the multiple layer glass panels used for constructing, forexample, the windshield, sun or moon roof, and side and rear windows, ofa vehicle are critical not only for the performance of those panels, butalso for the overall performance of the vehicle itself.

Recent trends toward more fuel efficient vehicles have brought aboutdemand for lighter weight vehicles. One way of reducing vehicle weighthas been to reduce the amount of glass by using thinner glass sheets.For example, for a windshield having a surface area of 1.4 m², reducingthe thickness of one of the panels by about 0.5 mm can result in aweight reduction of over 10 percent, all other things being equal.

One approach to thinner multiple layer panels has been to use an“asymmetric” glass configuration, wherein one of the panels is thinnerthan the other. Thinner glass panels with symmetric configurations havealso been used. However, the asymmetric configurations are more oftenemployed and involve using an “outboard” glass panel (i.e., the glasspanel facing outside of the vehicle cabin) with a traditional 2.0 mm to2.3 mm thickness and a thinner “inboard” glass panel (i.e., the glasspanel facing the interior of the cabin). This is to ensure adequatestrength and impact resistance against rocks, gravel, sand, and otherroad debris to which the outboard panel would be subjected to duringuse. Typically, however, these asymmetric panels retain a combined glassthickness of at least 3.7 mm in order to maintain properties such asdeflection stiffness, glass bending strength, glass edge strength, glassimpact strength, roof strength, and torsional rigidity within acceptableranges.

Further, because asymmetric configurations are formed by utilizing athinner inboard glass sheet, the sound insulation properties of thesepanels are poorer than similar panels utilizing thicker glass.Therefore, in order to minimize road noise and other disturbances withinthe cabin, interlayers used to form asymmetric multiple layer panels aregenerally interlayers having acoustic properties (i.e., acousticinterlayers). Conventional, non-acoustic interlayers do not providesufficient sound insulation for most applications.

Thus, a need exists for a multiple layer glass panel that includes theoptimal glass thickness, while still exhibiting sufficient strength,rigidity, and acoustic performance. Desirably, such a panel could bewidely used in a variety of automotive, aerospace, and architecturalapplications.

SUMMARY

One embodiment of the present invention concerns a multiple layer panelcomprising: a first substrate having a first nominal thickness; a secondsubstrate having a second nominal thickness, wherein said second nominalthickness is at least 0.1 mm less than said first nominal thickness; anda multiple layer interlayer disposed between and in contact with each ofsaid first and said second substrates, wherein said multiple layerinterlayer comprises: a first polymer layer comprising a firstpoly(vinyl acetal) resin and at least one plasticizer; and a secondpolymer layer adjacent to and in contact with said first polymer layer,wherein said second polymer layer comprises a second poly(vinyl acetal)resin and at least one plasticizer, wherein said first and said secondpoly(vinyl acetal) resins have respective first and second residualhydroxyl contents, and wherein said second residual hydroxyl content isat least 2 weight percent different than said first residual hydroxylcontent, wherein the ratio of said second nominal thickness to saidfirst nominal thickness is in the range of from at least 0.23:1 to lessthan 1:1, and wherein the sum of said first and said second nominalthicknesses is less than 3.7 mm.

Another embodiment of the present invention concerns a multiple layerpanel comprising: a first substrate having a first nominal thickness; asecond substrate having a second nominal thickness, wherein said secondnominal thickness is less than 1.8 mm; and an interlayer disposedbetween and in contact with each of said first and said secondsubstrates, wherein said interlayer comprises a first polymer layercomprising a first poly(vinyl acetal) resin and at least oneplasticizer, wherein the ratio of said second nominal thickness to saidfirst nominal thickness is in the range of from at least 0.23:1 to lessthan 1:1, wherein the sum of said first and said second nominalthicknesses is less than 3.7 mm and wherein said multiple layer panelexhibits a sound transmission loss at the coincident frequency, measuredaccording to ASTM E90, of at least 34 dB.

Yet another embodiment of the present invention concerns a multiplelayer panel comprising: a first substrate having a first nominalthickness; a second substrate having a second nominal thickness, whereinsaid second nominal thickness is at least 0.1 mm less than said firstnominal thickness; and an interlayer disposed between and in contactwith each of said first and said second substrates, wherein saidinterlayer comprises a first polymer layer comprising a first poly(vinylacetal) resin and at least one plasticizer, wherein the ratio of saidsecond nominal thickness to said first nominal thickness is in the rangeof from at least 0.23:1 to less than 1:1, wherein the sum of the firstand second nominal thicknesses is greater than 4.6 mm, and wherein saidmultiple layer panel exhibits a sound transmission loss at thecoincident frequency, measured according to ASTM E90, of at least 34 dB.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described in detailbelow with reference to the attached drawing Figures, wherein:

FIG. 1 is a cross-sectional view of a tapered interlayer configured inaccordance with one embodiment of the present invention, where variousfeatures of the tapered interlayer are labeled for ease of reference;

FIG. 2 is a cross-sectional view of a tapered interlayer having atapered zone that extends over the entire width of the interlayer, wherethe entire tapered zone has a constant wedge angle and a linearthickness profile;

FIG. 3 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer and aflat edge zone that extends over part of the width of the interlayer,where the tapered zone includes a constant angle zone and a variableangle zone;

FIG. 4 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone includes a constant angle zone andtwo variable angle zones;

FIG. 5 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone is formed entirely of a variableangle zones having a curved thickness profile;

FIG. 6 is a cross-sectional view of a tapered interlayer having atapered zone that extends over the entire width of the interlayer, wherethe tapered includes three constant angle zones spaced from one anotherby two variable angle zones;

FIG. 7 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone includes three constant angle zoneand four variable angle zones;

FIG. 8a is a plan view of a tapered interlayer configured for use in avehicle windshield, where the thickness provide of the interlayer issimilar to the thickness profile of the interlayer depicted in FIG. 2;

FIG. 8b is a cross-sectional view of the interlayer of FIG. 8a , showingthe thickness profile of the interlayer;

FIG. 9 is a graph of the sound transmission loss of several multiplelayer panels formed and tested as described in Example 1;

FIG. 10 is a diagram showing the experimental set up used to conduct thethree-point bending test;

FIG. 11 is a graphical representation of the load versus deflection of atest panel subjected to the three-point bending test; and

FIG. 12 is a graph of the sound transmission loss at the coincidentfrequency as a function of glass symmetry for several panels preparedand tested as described in Example 2.

DETAILED DESCRIPTION

The present invention relates generally to multiple layer panels thatcomprise a pair of substrates and an acoustic interlayer laminatedtherebetween. In some embodiments, the multiple layer panels of thepresent invention may have an asymmetric glass configuration, such thatone of the substrates has a thickness different than the other. Despitethis difference in thickness, however, multiple layer panels configuredaccording to embodiments of the present invention may still exhibitsufficient strength, rigidity, and acoustic performance, so that thepanels may be employed in a wide range of applications, including avariety of automotive, architectural, and aeronautical applications.

Multiple layer panels as described herein generally comprise at least afirst substrate, a second substrate, and an interlayer disposed betweenand in contact with each of the first and second substrates. Each of thefirst and second substrates can be formed of a rigid material, such asglass, and may be formed from the same, or from different, materials. Insome embodiments, at least one of the first and second substrates can bea glass substrate, while, in other embodiments, at least one of thefirst and second substrates can be formed of another material including,for example, a rigid polymer such as polycarbonate, acrylic, polyesters,copolyesters, and combinations thereof. Typically, neither of the firstor second substrates are formed from softer polymeric materialsincluding thermoplastic polymer materials as described in detailshortly.

In some embodiments, at least one of the first and second substrates maycomprise a glass substrate. Any suitable type of glass may be used toform such a substrate, and, in some embodiments, the glass may beselected from the group consisting of alumina-silicate glass,borosilicate glass, quartz or fused silica glass, and soda lime glass.The glass substrate, when used, may be annealed, thermally-strengthenedor tempered, chemically-tempered, etched, coated, or strengthened by ionexchange, or it may have been subjected to one or more of thesetreatments. The glass itself may be rolled glass, float glass, or plateglass. When the first and second substrates are glass substrates, thetype of glass used to form each may be the same or it may be different.

The first and second substrates can have any suitable thickness. In someembodiments, the nominal thickness of the first and/or second substratescan be at least about 0.4, at least about 0.5, at least about 0.6, atleast about 0.7, at least about 0.8, at least about 0.9, at least about1.0, at least about 1.1, at least about 1.2, at least about 1.3, atleast about 1.4, at least about 1.5, at least about 1.6, at least about1.7, at least about 1.8, at least about 1.9, at least about 2.0, atleast about 2.1, at least about 2.2 mm and/or less than about 3.2, lessthan about 3.1, less than about 3.0, less than about 2.9, less thanabout 2.8, less than about 2.7, less than about 2.6, less than about2.5, less than about 2.4, less than about 2.3, less than about 2.2, lessthan about 2.1, less than about 2.0, less than about 1.9, less thanabout 1.8, less than about 1.7, less than about 1.6, less than about1.5, less than about 1.4, less than about 1.3, less than about 1.2, lessthan about 1.1, or less than about 1.0 mm.

Additionally, or in the alternative, the first and/or second substratescan have a nominal thickness of at least about 2.3, at least about 2.4,at least about 2.5, at least about 2.6, at least about 2.7, at leastabout 2.8, at least about 2.9, at least about 3.0 and/or less than about12.5, less than about 12, less than about 11.5, less than about 11, lessthan about 10.5, less than about 10, less than about 9.5, less thanabout 9, less than about 8.5, less than about 8, less than about 7.5,less than about 7, less than about 6.5, less than about 6, less thanabout 5.9, less than about 5.8, less than about 5.7, less than about5.6, less than about 5.5, less than about 5.4, less than about 5.3, lessthan about 5.2, less than about 5.1, less than about 5.0, less thanabout 4.9, less than about 4.8, less than about 4.7, less than about4.6, less than about 4.5, less than about 4.4, less than about 4.3, lessthan about 4.2, less than about 4.1, or less than about 4.0 mm.

According to some embodiments, the multiple layer panel may include twosubstrates having the same nominal thickness. Such embodiments may bereferred to as “symmetric configurations,” because the ratio of thenominal thickness of one substrate to the nominal thickness of the othersubstrate equals 1.

In other embodiments, a multiple layer panel as described herein mayinclude two substrates having different nominal thicknesses. Suchembodiments, also referred to as “asymmetric configurations,” arecharacterized in that the ratio of the nominal thickness of the thinnersubstrate to the nominal thickness of the thicker substrate is lessthan 1. As used herein, the term “symmetry” refers to the ratio of thenominal thickness of the thinner substrate to the nominal thickness ofthe thicker substrate. In some embodiments, multiple layer panels asdescribed herein can have a symmetry of at least about 0.20, at leastabout 0.23, at least about 0.25, at least about 0.30, at least about0.35, at least about 0.40, at least about 0.45, at least about 0.50, atleast about 0.55, at least about 0.60, at least about 0.65, at leastabout 0.70, at least about 0.75 and/or less than about 1, not more thanabout 0.99, not more than about 0.97, not more than about 0.95, not morethan about 0.90, not more than about 0.85, not more than about 0.80, notmore than about 0.75, not more than about 0.70, not more than about0.65, not more than about 0.60, not more than about 0.55, not more thanabout 0.50, not more than about 0.45, not more than about 0.40, not morethan about 0.35, not more than about 0.30.

When the multiple layer panel has an asymmetric configuration, thedifference between the nominal thickness of the thicker substrate andthe nominal thickness of the thinner substrate can be at least about 0.1mm. In some embodiments, the nominal thickness of the thicker substratecan be at least about 0.2, at least about 0.3, at least about 0.4, atleast about 0.5, at least about 0.6, at least about 0.7, at least about0.8 mm thicker than the nominal thickness of the thinner substrate.Additionally, or in the alternative, the nominal thickness of thethicker substrate can be not more than about 7, not more than about 6,not more than about 5, not more than about 4, not more than about 3, notmore than about 2, not more than about 1.5, not more than about 1, notmore than about 0.9, not more than about 0.8, not more than about 0.7,not more than about 0.6, not more than about 0.5, not more than about0.4, or not more than about 0.3 mm thicker than the nominal thickness ofthe thinner substrate.

The sum of the nominal thicknesses of the first and second substrates,respectively (also referred to herein as the “combined glass thickness”)can be thinner than, or thicker than, conventional multiple layerpanels. Typically, conventional commercially-available multiple layerpanels have combined glass thicknesses in the range of from 3.7 mm to4.6 mm. In contrast, according to some embodiments of the presentinvention, the sum of the nominal thicknesses of the first and secondsubstrates can be less than 3.7, less than about 3.6, less than about3.5, less than about 3.4, less than about 3.3, or less than about 3.2mm. In all cases, the sum of the nominal thicknesses of the first andsecond substrates can be at least about 0.9, at least about 1.2, atleast about 1.5, at least about 2.0, at least about 2.5, at least about3.0, at least about 3.1, at least about 3.2 mm, at least about 3.3, atleast about 3.4, or at least about 3.5 mm.

Alternatively, or in addition, the sum of the nominal thicknesses of thefirst and second substrates can be greater than 4.6, greater than about4.7, greater than about 4.8, greater than about 4.9, greater than about5.0, greater than about 5.2, greater than about 5.5, greater than about5.7, greater than about 6.0, greater than about 6.2, greater than about6.5, greater than about 6.7, greater than about 7.0, greater than about7.2, greater than about 7.5, greater than about 7.7, greater than about8.0, greater than about 8.2, greater than about 8.5, greater than about8.7, greater than about 9.0, greater than about 9.5, greater than about10.0, greater than about 10.5, greater than about 11.0, greater thanabout 11.5, greater than about 12.0, greater than about 12.5, greaterthan about 13.0, greater than about 13.5, greater than about 14.0,greater than about 14.5, or greater than about 15.0 mm.

The specific glass configuration may be selected depending on theultimate end use of the multiple layer panel. For example, in someembodiments wherein the multiple layer panel is utilized in automotiveapplications, the nominal thickness of one of the substrates can be inthe range of from 0.4 to 1.8 mm, from 0.5 to 1.7 mm, or from 0.6 to 1.4mm, while the nominal thickness of the other substrate can have anominal thickness in the range of from 0.5 to 2.9 mm, from 0.6 to 2.8mm, from 1.0 to 2.4, or from 1.6 to 2.4 mm. The sum of the thicknessesof the substrates can be less than 3.7, less than 3.6, less than 3.5, orless than 3.4 mm, and the ratio of the nominal thickness of the thinnersubstrate to the nominal thickness of the thicker substrate can be inthe range of from 0.23 to less than 1, from 0.25 to 0.75, or from 0.3 to0.60.

In other embodiments wherein the multiple layer panel is utilized inaeronautical or architectural applications, the nominal thickness of oneof the substrates may be in the range of from 2.2 to 12.5 mm, from 2.6to 8 mm, or from 2.8 to 5 mm, while the nominal thickness of the othersubstrate may be in the range of from 1.6 to 12.4 mm, from 1.8 to 7.5mm, or from 2.3 to 5 mm. The sum of the thicknesses of the substrates inthese embodiments can be greater than 4.7 mm, greater than 5 mm, greaterthan 5.5 mm, or greater than 6 mm, with a symmetry in the range of from0.23 to less than 1, from 0.25 to 0.75, or from 0.3 to 0.60.

In addition to the substrates, multiple layer panels as described hereininclude at least one polymeric interlayer disposed between and incontact with each of the first and second substrates. As used herein,the term “interlayer” refers to a single or multiple layer polymer sheetsuitable for use in forming multiple layer panels. As used herein, theterms “single layer” and “monolithic” refer to interlayers formed of onesingle polymer layer, while the terms “multiple layer” or “multilayer”refer to interlayers having two or more polymer layers adjacent to andin contact with one another. Each polymer layer of an interlayer mayinclude one or more polymeric resins, optionally combined with one ormore plasticizers, which have been formed into a sheet by any suitablemethod. One or more of the polymer layers in an interlayer may furtherinclude additional additives, although these are not required.

Examples of suitable thermoplastic polymers can include, but are notlimited to, poly(vinyl acetal) resins, polyurethanes (PU),poly(ethylene-co-vinyl acetate) resins (EVA), polyvinyl chlorides (PVC),poly(vinylchloride-co-methacrylate), polyethylenes, polyolefins,ethylene acrylate ester copolymers, poly(ethylene-co-butyl acrylate),silicone elastomers, epoxy resins, and acid copolymers such asethylene/carboxylic acid copolymers and ionomers thereof, derived fromany of the previously-listed polymers, and combinations thereof. In someembodiments, one or more layers of a multiple layer interlayer caninclude a thermoplastic polymer can be selected from the groupconsisting of poly(vinyl acetal) resins, polyvinyl chloride, andpolyurethanes. In certain embodiments, one or more of the polymer layerscan include at least one poly(vinyl acetal) resin. Although generallydescribed herein with respect to poly(vinyl acetal) resins, it should beunderstood that one or more of the above polymer resins could beincluded with, or in the place of, the poly(vinyl acetal) resinsdescribed below in accordance with various embodiments of the presentinvention.

Polyurethanes can have different hardnesses. An exemplary polyurethanepolymer has a Shore A hardness less than 85 per ASTM D-2240. Examples ofpolyurethane polymers are AG8451 and AG5050, aliphatic isocyanatepolyether based polyurethanes having glass transition temperatures lessthan 20° C. (commercially available from Thermedics Inc. of Woburn,Mass.). EVA polymers can contain various amounts of vinyl acetategroups. The desirable vinyl acetate content is generally from about 10to about 90 mol %. EVA with lower vinyl acetate content can be used forsound insulation at low temperatures. The ethylene/carboxylic acidcopolymers are generally poly(ethylene-co-methacrylic acid) andpoly(ethylene-co-acrylic acid) with the carboxylic acid content from 1to 25 mole %. Ionomers of ethylene/carboxylic acid copolymers can beobtained by partially or fully neutralizing the copolymers with a base,such as the hydroxide of alkali (sodium for example) and alkaline metals(magnesium for example), ammonia, or other hydroxides of transitionmetals such as zinc. Examples of ionomers of that are suitable includeSurlyn® ionomers resins (commercially available from DuPont ofWilmington, Del.).

Examples of exemplary multilayer interlayer constructs include, but arenot limited to, PVB//PVB//PVB and PVnB//PVisoB//PVnB, where the PVB(polyvinyl butyral), PVnB (polyvinyl n-butyral) and/or PVisoB (polyvinyliso-butyral) layers comprise a single resin or two or more resins havingdifferent residual hydroxyl contents or different polymer compositions;PVC//PVB//PVC, PU//PVB//PU, Ionomer//PVB//Ionomer, Ionomer//PU//Ionomer,Ionomer//EVA//Ionomer, Ionomer//Ionomer//Ionomer, where the core layerPVB (including PVisoB), PU, EVA or ionomer comprises a single resin ortwo or more resins having different glass transitions. Alternatively,the skin and core layers may all be PVB, PVnB and/or PVisoB using thesame or different starting resins. Other combinations of resins andpolymers will be apparent to those skilled in the art. In general, PVBresin refers to PVnB or PVisoB or combinations of PVnB and PVisoB.

Thermoplastic polymer resins may be formed by any suitable method. Whenthe thermoplastic polymer resins include poly(vinyl acetal) resins, suchresins may be formed by acetalization of poly(vinyl alcohol) with one ormore aldehydes in the presence of a catalyst according to known methodssuch as, for example, those described in U.S. Pat. Nos. 2,282,057 and2,282,026, as well as “Vinyl Acetal Polymers,” in the Encyclopedia ofPolymer Science & Technology, 3^(rd) ed., Volume 8, pages 381-399, by B.E. Wade (2003). The resulting poly(vinyl acetal) resins may include atleast about 50, at least about 60, at least about 70, at least about 75,at least about 80, at least about 85, at least about 90 weight percentof residues of at least one aldehyde, measured according to ASTM D-1396as the percent acetalization of the resin. The total amount of aldehyderesidues in a poly(vinyl acetal) resin can be collectively referred toas the acetal content, with the balance of the poly(vinyl acetal) resinbeing residual hydroxyl groups (as vinyl hydroxyl groups) and residualester groups (as vinyl acetate groups), which will be discussed infurther detail below.

Suitable poly(vinyl acetal) resins may include residues of any aldehydeand, in some embodiments, may include residues of at least one C₄ to C₈aldehyde. Examples of suitable C₄ to C₈ aldehydes can include, forexample, n-butyraldehyde, i-butyraldehyde, 2-methylvaleraldehyde,n-hexyl aldehyde, 2-ethylhexyl aldehyde, n-octyl aldehyde, andcombinations thereof. One or more of the poly(vinyl acetal) resinsutilized in the layers and interlayers described herein can include atleast about 20, at least about 30, at least about 40, at least about 50,at least about 60, or at least about 70 weight percent of residues of atleast one C₄ to C₈ aldehyde, based on the total weight of aldehyderesidues of the resin. Alternatively, or in addition, the poly(vinylacetal) resin may include not more than about 99, not more than about95, not more than about 90, not more than about 85, not more than about80, not more than about 75, not more than about 70, or not more thanabout 65 weight percent of at least one C₄ to C₈ aldehyde. The C₄ to C₈aldehyde may be selected from the group listed above, or it can beselected from the group consisting of n-butyraldehyde, i-butyraldehyde,2-ethylhexyl aldehyde, and combinations thereof. In other embodiments,the poly(vinyl acetal) resin may comprise residues of other aldehydes,including, but not limited to, cinnamaldehyde, hexylcinnamaldehyde,benzaldehyde, hydrocinnamaldehyde, 4-chlorobenzaldehyde,4-t-butylphenylacetaldehyde, propionaldehyde, 2-phenylpropionaldehyde,and combinations thereof, alone or in combination with one or more ofthe C₄ to C₈ aldehydes described herein.

In various embodiments, the poly(vinyl acetal) resin may be a poly(vinylbutyral) (PVB) resin that primarily comprises residues ofn-butyraldehyde, and may, for example, include not more than about 30,not more than about 20, not more than about 10, not more than about 5,not more than about 2, or not more than 1 weight percent of residues ofan aldehyde other than n-butyraldehyde. Typically, the aldehyde residuesother than n-butyraldehyde present in poly(vinyl butyral) resins mayinclude iso-butyraldehyde, 2-ethylhexyl aldehyde, and combinationsthereof. When the poly(vinyl acetal) resin comprises a poly(vinylbutyral) resin, the weight average molecular weight of the resin can beat least about 30,000, at least about 50,000, at least about 80,000, atleast about 100,000, at least about 130,000, at least about 150,000, atleast about 175,000, at least about 200,000, at least about 300,000, orat least about 400,000 Daltons, measured by size exclusionchromatography using low angle laser light scattering (SEC/LALLS) methodof Cotts and Ouano.

In general, poly(vinyl acetal) resins can be produced by hydrolyzing apoly(vinyl acetate) to poly(vinyl alcohol), and then acetalizing thepoly(vinyl alcohol) with one or more of the above aldehydes to form apoly(vinyl acetal) resin. In the process of hydrolyzing the poly(vinylacetate), not all the acetate groups are converted to hydroxyl groups,and, as a result, residual acetate groups remain on the resin.Similarly, in the process of acetalizing the poly(vinyl alcohol), notall of the hydroxyl groups are converted to acetal groups, which alsoleaves residual hydroxyl groups on the resin. As a result, mostpoly(vinyl acetal) resins include both residual hydroxyl groups (asvinyl hydroxyl groups) and residual acetate groups (as vinyl acetategroups) as part of the polymer chain. As used herein, the terms“residual hydroxyl content” and “residual acetate content” refer to theamount of hydroxyl and acetate groups, respectively, that remain on aresin after processing is complete. Both the residual hydroxyl contentand the residual acetate content are expressed in weight percent, basedon the weight of the polymer resin, and are measured according to ASTMD-1396.

The poly(vinyl acetal) resins utilized in one or more polymer layers asdescribed herein may have a residual hydroxyl content of at least about8, at least about 9, at least about 10, at least about 11, at leastabout 12, at least about 13, at least about 14, at least about 15, atleast about 16, at least about 17, at least about 18, at least about18.5, at least about 19, at least about 20, at least about 21, at leastabout 22, at least about 23, at least about 24, at least about 25, atleast about 26, at least about 27, at least about 28, at least about 29,at least about 30, at least about 31, at least about 32, or at leastabout 33 weight percent. Additionally, or in the alternative, thepoly(vinyl acetal) resin or resins utilized in polymer layers of thepresent invention may have a residual hydroxyl content of not more thanabout 45, not more than about 43, not more than about 40, not more thanabout 37, not more than about 35, not more than about 34, not more thanabout 33, not more than about 32, not more than about 31, not more thanabout 30, not more than about 29, not more than about 28, not more thanabout 27, not more than about 26, not more than about 25, not more thanabout 24, not more than about 23, not more than about 22, not more thanabout 21, not more than about 20, not more than about 19, not more thanabout 18.5, not more than about 18, not more than about 17, not morethan about 16, not more than about 15, not more than about 14, not morethan about 13, not more than about 12, not more than about 11, or notmore than about 10 weight percent.

In some embodiments, one or more polymer layers can include at least onepoly(vinyl acetal) resin having a residual hydroxyl content of at leastabout 20, at least about 21, at least about 22, at least about 23, atleast about 24, at least about 25, at least about 26, at least about 27,at least about 28, at least about 29, or at least about 30 weightpercent and/or not more than about 45, not more than about 43, not morethan about 40, not more than about 37, not more than about 35, not morethan about 34, not more than about 33, or not more than about 32 weightpercent.

In some embodiments, one or more polymer layers can include at least onepoly(vinyl acetal) resin having a residual hydroxyl content of at leastabout 8, at least about 9, at least about 10, at least about 11, or atleast about 12 and/or not more than about 17, not more than about 16,not more than about 15, or not more than about 14 weight percent.

When a polymer layer or interlayer includes more than one type ofpoly(vinyl acetal) resin, each of the poly(vinyl acetal) resins may havesubstantially the same residual hydroxyl contents, or one or more of thepoly(vinyl acetal) resins may have a residual hydroxyl contentsubstantially different from one or more other poly(vinyl acetal)resins. Various embodiments of several interlayers that include morethan one poly(vinyl acetal) resin are discussed in further detail below.

One or more poly(vinyl acetal) resins used in interlayers according tothe present invention may have a residual acetate content of not morethan about 25, not more than about 20, not more than about 18, not morethan about 15, not more than about 12, not more than about 10, not morethan about 8, not more than about 6, not more than about 4, not morethan about 3, or not more than about 2 weight percent. Alternatively, orin addition, at least one poly(vinyl acetal) resin used in a polymerlayer or interlayer as described herein can have a residual acetatecontent of at least about 3, at least about 4, at least about 5, atleast about 6, at least about 7, at least about 8, at least about 9, atleast about 10, at least about 12, at least about 14 weight percent ormore. When a polymer layer or interlayer includes two or more poly(vinylacetal) resins, the resins may have substantially the same residualacetate content, or one or more resins may have a residual acetatecontent different from the residual acetate content of one or more otherpoly(vinyl acetal) resins.

The present invention discloses multiple layer panels comprising anacoustic polymer interlayer. In embodiments, the polymer interlayer canbe either a monolithic acoustic interlayer or a multilayer acousticinterlayer or a combination of monolithic and multilayer interlayers.Monolithic or single layer polymer interlayers having acoustic or soundinsulation properties can be produced by mixing a thermoplastic polymerresin and optionally a plasticizer, and extruding the mixture to form apolymer interlayer. The resultant acoustic polymer interlayer typicallyexhibits at least one glass transition temperature, T_(g), of 25° C. orless. In embodiments, the thermoplastic resin is may be one of thethermoplastic polymers previously mentioned. In other embodiments, thethermoplastic resin is a poly(vinyl acetal) resin, such as poly(vinylbutyral) (PVB). Monolithic or single layer acoustic PVB interlayers canbe produced by mixing PVB resin having a low residual hydroxyl content(weight percent PVOH), such as 17 weight percent or less, with higheramounts of a plasticizer, such as triethylene glycoldi-(2-ethylhexanoate) (3GEH), and extruding the mixture to form apolymer interlayer. Alternatively, monolithic or single layer PVBinterlayers having acoustic properties can be produced by mixing PVBresin having a high residual hydroxyl content, such as 18 weight percentor more, with a high amount of a plasticizer, or a mixture ofplasticizers in which at least one plasticizer in the mixture is moreefficient in plasticizing PVB resin than conventional plasticizer (suchas 3GEH). Multiple layer interlayers (comprising at least two adjacentpolymer layers in contact with each other) that exhibit acousticproperties and reduce sound transmission through a multiple layer glasspanel can be produced in such a way that there are various compositionalpermutations or differences between the two or more layers as furtherdescribed herein.

The polymeric resin or resins utilized in polymer layers and interlayersas described herein may comprise one or more thermoplastic polymerresins. In some embodiments, the thermoplastic resin or resins may bepresent in the polymer layer in an amount of at least about 50, at leastabout 55, at least about 60, at least about 65, at least about 70, atleast about 75, at least about 80, at least about 85, at least about 90,or at least about 95 weight percent, based on the total weight of thepolymer layer. When two or more resins are present, each may be presentin an amount of at least about 0.5, at least about 1, at least about 2,at least about 5, at least about 10, at least about 15, at least about20, at least about 25, at least about 30, at least about 35, at leastabout 40, at least about 45, or at least about 50 weight percent, basedon the total weight of the polymer layer or interlayer.

One or more polymer layers as described herein may also include at leastone plasticizer. When present, the plasticizer content of one or morepolymer layers can be at least about 2, at least about 5, at least about6, at least about 8, at least about 10, at least about 15, at leastabout 20, at least about 25, at least about 30, at least about 35, atleast about 40, at least about 45, at least about 50, at least about 55,at least about 60, at least about 65, at least about 70, at least about75, at least about 80 parts per hundred resin (phr) and/or not more thanabout 120, not more than about 110, not more than about 105, not morethan about 100, not more than about 95, not more than about 90, not morethan about 85, not more than about 75, not more than about 70, not morethan about 65, not more than about 60, not more than about 55, not morethan about 50, not more than about 45, not more than about 40, or notmore than about 35 phr. In some embodiments, one or more polymer layerscan have a plasticizer content of not more than 35, not more than about32, not more than about 30, not more than about 27, not more than about26, not more than about 25, not more than about 24, not more than about23, not more than about 22, not more than about 21, not more than about20, not more than about 19, not more than about 18, not more than about17, not more than about 16, not more than about 15, not more than about14, not more than about 13, not more than about 12, not more than about11, or not more than about 10 phr.

As used herein, the term “parts per hundred resin” or “phr” refers tothe amount of plasticizer present per one hundred parts of resin, on aweight basis. For example, if 30 grams of plasticizer were added to 100grams of a resin, the plasticizer content would be 30 phr. If thepolymer layer includes two or more resins, the weight of plasticizer iscompared to the combined amount of all resins present to determine theparts per hundred resin. Further, when the plasticizer content of alayer or interlayer is provided herein, it is provided with reference tothe amount of plasticizer in the mix or melt that was used to producethe layer or interlayer, unless otherwise specified.

For layers of unknown plasticizer content, the plasticizer content canbe determined via a wet chemical method in which an appropriate solvent,or mixture of solvents, is used to extract the plasticizer from thepolymer layer or interlayer. Prior to extracting the plasticizer, theweight of the sample layer is measured and compared with the weight ofthe layer from which the plasticizer has been removed after extraction.Based on this difference, the weight of plasticizer can be determinedand the plasticizer content, in phr, calculated. For multiple layerinterlayers, the polymer layers can be physically separated from oneanother and individually analyzed according to the above procedure.

Although not wishing to be bound by theory, it is understood that, for agiven type of plasticizer, the compatibility of the plasticizer in thepoly(vinyl acetal) resin may be correlated to the residual hydroxylcontent of the resin. More particularly, poly(vinyl acetal) resinshaving higher residual hydroxyl contents may generally have a reducedplasticizer compatibility or capacity, while poly(vinyl acetal) resinswith a lower residual hydroxyl content may exhibit an increasedplasticizer compatibility or capacity. Generally, this correlationbetween the residual hydroxyl content of a polymer and its plasticizercompatibility/capacity can be manipulated in order to facilitateaddition of the proper amount of plasticizer to the polymer resin and tostably maintain differences in plasticizer content between multiplelayers within an interlayer. A similar correlation may also exist forthe compatibility of the plasticizer and residual acetate content in thepoly(vinyl acetal) resin.

Any suitable plasticizer can be used in the polymer layers describedherein. The plasticizer may have a hydrocarbon segment of at least about6 and/or not more than about 30, not more than about 25, not more thanabout 20, not more than about 15, not more than about 12, or not morethan about 10 carbon atoms. In various embodiments, the plasticizer isselected from conventional plasticizers, or a mixture of two or moreconventional plasticizers. In some embodiments, the conventionalplasticizer, which has refractive index of less than about 1.450, mayinclude, triethylene glycol di-(2-ethylhexanoate) (“3GEH”), triethyleneglycol di-(2-ethylbutyrate), tetraethylene glycol di-(2-ethylhexanoate)(“4GEH”), triethylene glycol diheptanoate, tetraethylene glycoldiheptanoate, dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate,diisononyl adipate, heptylnonyl adipate, di(butoxyethyl) adipate,bis(2-(2-butoxyethoxy)ethyl) adipate, dibutyl sebacate, dioctylsebacate, butyl ricinoleate, castor oil, triethyl glycol ester ofcoconut oil fatty acids, and oil modified sebacic alkyd resins. In someembodiments, the conventional plasticizer is 3GEH (Refractiveindex=1.442 at 25° C.).

In some embodiments, other plasticizers known to one skilled in the artmay be used, such as a plasticizer with a higher refractive index (i.e.,a high refractive index plasticizer). As used herein, a “high refractiveindex plasticizer” is a plasticizer having a refractive index of atleast about 1.460. As used herein, the refractive index (also known asindex of refraction) of a plasticizer or a resin used in the entirety ofthis disclosure is either measured in accordance with ASTM D542 at awavelength of 589 nm and 25° C. or reported in literature in accordancewith ASTM D542. In various embodiments, the refractive index of theplasticizer is at least about 1.460, or greater than about 1.470, orgreater than about 1.480, or greater than about 1.490, or greater thanabout 1.500, or greater than 1.510, or greater than 1.520, for both coreand skin layers. In some embodiments, the high refractive indexplasticizer(s) is used in conjunction with a conventional plasticizer,and in some embodiments, if included, the conventional plasticizer is3GEH, and the refractive index of the plasticizer mixture is at least1.460. Examples of suitable plasticizers include, but are not limitedto, dipropylene glycol dibenzoate, tripropylene glycol dibenzoate,polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexylbenzoate, diethylene glycol benzoate, butoxyethyl benzoate,butoxyethyoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propyleneglycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), di-(butoxyethyl) terephthalate,di-(butoxyethyoxyethyl) terephthalate, dibutoxy ethyl phthalate, diethylphthalate, dibutyl phthalate, trioctyl phosphate, phenyl ethers ofpolyethylene oxide rosin derivatives, and tricresyl phosphate, andmixtures thereof. In some embodiments, the plasticizer may comprise, orconsist of, a mixture of conventional and high refractive indexplasticizers.

Additionally, at least one polymer layer may also include other types ofadditives that can impart particular properties or features to thepolymer layer or interlayer. Such additives can include, but are notlimited to, dyes, pigments, stabilizers such as ultraviolet stabilizers,antioxidants, anti-blocking agents, flame retardants, IR absorbers orblockers such as indium tin oxide, antimony tin oxide, lanthanumhexaboride (LaB₆) and cesium tungsten oxide, processing aides, flowenhancing additives, lubricants, impact modifiers, nucleating agents,thermal stabilizers, UV absorbers, dispersants, surfactants, chelatingagents, coupling agents, adhesives, primers, reinforcement additives,and fillers. Specific types and amounts of such additives may beselected based on the final properties or end use of a particularinterlayer.

Additionally, various adhesion control agents (“ACAs”) can also be usedin one or more polymer layers in order to control the adhesion of thelayer or interlayer to a sheet of glass. In various embodiments, theamount of ACAs present in a resin composition, layer, or interlayer canbe at least about 0.003, at least about 0.01, at least about 0.025and/or not more than about 0.15, not more than about 0.10, not more thanabout 0.04 phr. Suitable ACAs can include, but are not limited to,residual sodium acetate, potassium acetate, magnesium bis(2-ethylbutyrate), magnesium bis(2-ethylhexanoate), and combinations thereof, aswell as the ACAs disclosed in U.S. Pat. No. 5,728,472.

Depending on the polymer type and layer composition, the polymer layersdescribed herein may exhibit a wide range of glass transitiontemperatures. In some embodiments, interlayers including two or morepolymers or polymer layers can exhibit two or more glass transitiontemperatures. The glass transition temperature (T_(g)) of a polymericmaterial is the temperature that marks the transition of the materialfrom a glass state to a rubbery state. The glass transition temperaturesof the polymer layers described herein were determined by dynamicmechanical thermal analysis (DMTA) according to the following procedure.A polymer sheet is molded into a sample disc of 25 millimeters (mm) indiameter. The polymer sample disc is placed between two 25-mm diameterparallel plate test fixtures of a Rheometrics Dynamic Spectrometer II.The polymer sample disc is tested in shear mode at an oscillationfrequency of 1 Hertz as the temperature of the sample is increased from−20 to 70° C., or other temperature range, at a rate of 2° C./minute.The position of the maximum value of tan delta (damping) plotted asdependent on temperature is used to determine the glass transitiontemperature. Experience indicates that the method is reproducible towithin +/−1° C.

Interlayers as described herein may include at least one polymer layerhaving a glass transition temperature of at least about −20, at leastabout −10, at least about −5, at least about −1, at least about 0, atleast about 1, at least about 2, at least about 5, at least about 10, atleast about 15, at least about 20, at least about 25, at least about 27,at least about 30, at least about 32, at least about 33, at least about35, at least about 36, at least about 37, at least about 38, or at leastabout 40° C. Alternatively, or in addition, the polymer layer can have aglass transition temperature of not more than about 45, not more thanabout 44, not more than about 43, not more than about 42, not more thanabout 41, not more than about 40, not more than about 39, not more thanabout 38, not more than about 37, not more than about 36, not more thanabout 35, not more than about 34, not more than about 33, not more thanabout 32, not more than about 30, not more than about 25, not more thanabout 20, not more than about 15, not more than about 10, not more thanabout 5, not more than about 2, not more than about 0, not more thanabout −1, or not more than about −5° C.

In some embodiments, one or more polymer layers may have a glasstransition temperature of at least about 30, at least about 32, at leastabout 33, at least about 35, at least about 36, at least about 37, atleast about 38, at least about 39, or at least about 40° C. and/or notmore than about 100, not more than about 90, not more than about 80, notmore than about 70, not more than about 60, not more than about 50, notmore than about 45, not more than about 44, not more than about 43, notmore than about 42, not more than about 41, not more than about 40, notmore than about 39, not more than about 38, or not more than about 37°C. Alternatively, or in addition, at least one polymer layer may have aglass transition temperature of at least about −10, at least about −5,at least about −2, at least about −1, at least about 0, at least about1, at least about 2, or at least about 5 and/or not more than about 25,not more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 2, not more than about 1, notmore than about 0, or not more than about −1° C. When a polymer layer orinterlayer includes two or more polymer layers, at least one of thelayers may have a glass transition temperature different from one ormore other polymer layers within the interlayer. Various embodiments ofmultiple layer interlayers will be discussed in further detail below.

According to some embodiments of the present invention, the interlayermay be a single layer, or monolithic, interlayer. In other embodiments,the interlayer may be a multiple layer interlayer comprising at least afirst polymer layer and a second polymer layer. In some embodiments, themultiple layer interlayer may also include a third polymer layer and thesecond polymer layer is adjacent to and in contact with each of thefirst and third polymer layers such that the second polymer layer issandwiched between the first and third polymer layers. As used herein,the terms “first,” “second,” “third,” and the like are used to describevarious elements, but such elements should not be unnecessarily limitedby these terms. These terms are only used to distinguish one elementfrom another and do not necessarily imply a specific order or even aspecific element. For example, an element may be regarded as a “first”element in the description and a “second” element in the claims withoutbeing inconsistent. Consistency is maintained within the description andfor each independent claim, but such nomenclature is not necessarilyintended to be consistent therebetween. Such three-layer interlayers maybe described as having at least one inner “core” layer sandwichedbetween two outer “skin” layers.

In some embodiments, each of the polymer layers in an interlayer caninclude a poly(vinyl acetal) resin. When the interlayer is a multiplelayer interlayer, it may include a first polymer layer comprising afirst poly(vinyl acetal) resin and a second polymer layer comprising asecond poly(vinyl acetal) resin. The first and second polymer layers canbe adjacent to one another or, optionally, may have one or moreintervening polymer layers therebetween.

When present, the first and second poly(vinyl acetal) resins of therespective first and second polymer layers can have differentcompositions. For example, in some embodiments, the first poly(vinylacetal) resin can have a residual hydroxyl content that is at leastabout 2, at least about 3, at least about 4, at least about 6, at leastabout 7, at least about 8, at least about 9, at least about 10, at leastabout 11, at least about 12, at least about 13, at least about 14, atleast about 15, at least about 16, at least about 17, at least about 18,at least about 19, at least about 20, at least about 21, at least about22, at least about 23, or at least about 24 weight percent differentthan the residual hydroxyl content of the second poly(vinyl acetal)resin.

Additionally, or in the alternative, the first poly(vinyl acetal) resincan have a residual acetate content that is at least about 2, at leastabout 3, at least about 4, at least about 5, at least about 6, at leastabout 7, at least about 8, at least about 9, at least about 10, at leastabout 11, at least about 12, at least about 13, at least about 15, atleast about 18, or at least about 20 weight percent different than theresidual acetate content of the second poly(vinyl acetal) resin. Inother embodiments, the first poly(vinyl acetal) resin can have aresidual acetate content that is not more than about 2, not more thanabout 1.5, not more than about 1, or not more than about 0.5 weightpercent different than the residual acetate content of the secondpoly(vinyl acetal) resin.

As used herein, the term “weight percent different” or “the difference .. . is at least . . . weight percent” refers to a difference between twogiven percentages, calculated by finding the absolute value of themathematical difference between the two numbers. A value that is“different” from a given value can be higher or lower than the givenvalue. For example, a first poly(vinyl acetal) resin having a residualhydroxyl content that is “at least 2 weight percent different than” theresidual hydroxyl content of a second poly(vinyl acetal) resin may havea residual hydroxyl content that is at least 2 weight percent higher orat least 2 weight percent lower than the second residual hydroxylcontent. For example, if the residual hydroxyl content of the exemplarysecond poly(vinyl acetal) resin is 14 weight percent, the residualhydroxyl content of the exemplary first poly(vinyl acetal) resin can beat least 16 weight percent (e.g., at least 2 weight percent higher) ornot more than 12 weight percent (e.g., at least 2 weight percent lower).

As a result of having different compositions, the portions of the layeror interlayer formed from the first poly(vinyl acetal) resin and thesecond poly(vinyl acetal) resin may have different properties, due to,for example, differences in plasticizer content. As describedpreviously, when two poly(vinyl acetal) resins having different residualhydroxyl contents are blended with a plasticizer(s), the plasticizerwill partition between the different resins, such that a higher amountof plasticizer is present in the layer formed from the lower residualhydroxyl content resin and less plasticizer is present in the portion ofthe layer including the higher residual hydroxyl content resin.Ultimately, a state of equilibrium is achieved between the two resins.The correlation between the residual hydroxyl content of a poly(vinylacetal) resin and plasticizer compatibility/capacity can facilitateaddition of a proper amount of plasticizer to the polymer resin. Such acorrelation also helps to stably maintain the difference in plasticizercontent between two or more layers when the plasticizer would otherwisemigrate from one to the other.

When the first and second poly(vinyl acetal) resins have differentresidual hydroxyl contents or have different residual acetate contents,the first and second polymer layers may also include different amountsof plasticizer. As a result, each of these portions may also exhibitdifferent properties, such as, for example, glass transitiontemperature. In some embodiments, the difference in plasticizer contentbetween adjacent first and second polymer layers can be at least about2, at least about 5, at least about 8, at least about 10, at least about12, or at least about 15 phr, measured as described above. In otherembodiments, the difference in plasticizer content between adjacentfirst and second polymer layers can be at least about 18, at least about20, at least about 25, at least about 30, at least about 35, at leastabout 40, at least about 45, at least about 50, at least about 55, atleast about 60, or at least about 65 phr.

In addition, or in the alternative, the difference between theplasticizer content of adjacent first and second polymer layers may benot more than about 40, not more than about 35, not more than about 30,not more than about 25, not more than about 20, not more than about 17,not more than about 15 or not more than about 12 phr. The values for theplasticizer content of each of the first and second polymer layers mayfall within one or more of the ranges provided above.

In some embodiments, the glass transition temperature of the firstpolymer layer can be at least about 3, at least about 5, at least about8, at least about 10, at least about 12, at least about 13, at leastabout 15, at least about 18, at least about 20, at least about 22, atleast about 25, at least about 30, at least about 35, or at least about40° C. different than the second polymer layer. The values for the glasstransition temperatures of each of the first and second polymer layersmay fall within one or more of the ranges provided above.

When the multiple layer interlayer includes three polymer layers, eachof the respective first, second, and third polymer layers can include atleast one poly(vinyl acetal) resin and an optional plasticizer of thetypes and in the amounts described in detail previously. According tosome embodiments, the second, inner polymer layer can include a resinhaving a residual hydroxyl content lower than the residual hydroxylcontents of the poly(vinyl acetal) resins in each of the first and thirdpolymer layers. Consequently, as the plasticizer partitions between thelayers, the second inner layer may have a glass transition temperaturelower than the glass transition temperatures of each of the first andthird outer polymer layers. Although not wishing to be bound by theory,it is understood that this type of configuration, wherein relatively“stiff” (i.e., higher glass transition temperature) outer polymer layersare sandwiching a “soft” (i.e., relatively low glass transitiontemperature) inner layer, may facilitate enhanced acoustic performancefrom the interlayer.

In some embodiments, the first and third outer polymer layers can havethe same as or similar compositions and/or properties. For example, insome embodiments, the poly(vinyl acetal) resin in the first polymerlayer can have a residual hydroxyl content within about 2, within about1, or within about 0.5 weight percent of the residual hydroxyl contentof the poly(vinyl acetal) resin in the third polymer layer. Similarly,the poly(vinyl acetal) resins in the first and third layer can haveresidual acetate contents within about 2, within about 1, or withinabout 0.5 weight percent of one another. Additionally, the first andthird outer polymer layers may have similar plasticizer contents and/ormay exhibit similar glass transition temperatures. For example, theplasticizer content of the first polymer layer can be less than 2, notmore than about 1, or not more than about 0.5 phr different than theplasticizer content of the third polymer layer, and/or the first andthird polymer layers can have glass transition temperatures that differby less than 2, not more than about 1, or not more than about 0.5° C.

The interlayers of the present invention can be formed according to anysuitable method. Exemplary methods can include, but are not limited to,solution casting, compression molding, injection molding, meltextrusion, melt blowing, and combinations thereof. Multilayerinterlayers including two or more polymer layers may also be producedaccording to any suitable method such as, for example, co-extrusion,blown film, melt blowing, dip coating, solution coating, blade, paddle,air-knife, printing, powder coating, spray coating, lamination, andcombinations thereof.

According to various embodiments of the present invention, the layers orinterlayers may be formed by extrusion or co-extrusion. In an extrusionprocess, one or more thermoplastic resins, plasticizers, and,optionally, one or more additives as described previously, can bepre-mixed and fed into an extrusion device. The extrusion device isconfigured to impart a particular profile shape to the thermoplasticcomposition in order to create an extruded sheet. The extruded sheet,which is at an elevated temperature and highly viscous throughout, canthen be cooled to form a polymeric sheet. Once the sheet has been cooledand set, it may be cut and rolled for subsequent storage,transportation, and/or use as an interlayer.

Co-extrusion is a process by which multiple layers of polymer materialare extruded simultaneously. Generally, this type of extrusion utilizestwo or more extruders to melt and deliver a steady volume throughput ofdifferent thermoplastic melts of different viscosities or otherproperties through a co-extrusion die into the desired final form. Thethickness of the multiple polymer layers leaving the extrusion die inthe co-extrusion process can generally be controlled by adjustment ofthe relative speeds of the melt through the extrusion die and by thesizes of the individual extruders processing each molten thermoplasticresin material.

The overall average thickness of interlayers according to variousembodiments of the present invention can be at least about 10, at leastabout 15, at least about 20, at least about 25, at least about 30, or atleast about 35 mils (1 mil=0.0254 mm) and/or not more than about 120,not more than about 90, not more than about 75, not more than about 60,not more than about 50, not more than about 45, not more than about 40,not more than about 35, or not more than about 32 mils. If theinterlayer is not laminated between two substrates, its averagethickness can be determined by directly measuring the thickness of theinterlayer using a caliper, or other equivalent device. If theinterlayer is laminated between two substrates, its thickness can bedetermined by subtracting the combined thickness of the substrates fromthe total thickness of the multiple layer panel.

In some embodiments, one or more polymer layers can have an averagethickness of at least about 1, at least about 2, at least about 3, atleast about 4, at least about 5, at least about 6, at least about 7, atleast about 8, at least about 9, or at least about 10 mils or more.Additionally, or in the alternative, one or more of the polymer layersin an interlayer as described herein can have an average thickness ofnot more than about 25, not more than about 20, not more than about 15,not more than about 12, not more than about 10, not more than about 8,not more than about 6, or not more than about 5 mils.

In some embodiments, the polymer layers or interlayers can comprise flatpolymer layers having substantially the same thickness along the length,or longest dimension, and/or width, or second longest dimension, of thesheet. In other embodiments, one or more layers of an interlayer can bewedge-shaped or can have a wedge-shaped profile, such that the thicknessof the interlayer changes along the length and/or width of the sheet andone edge of the layer or interlayer has a thickness greater than theother edge. When the interlayer is a multilayer interlayer, at leastone, at least two, or at least three (or more) of the layers of theinterlayer can be wedge-shaped. When the interlayer is a monolithicinterlayer, the polymer sheet can be flat or wedge shaped. Wedge-shapedinterlayers may be useful in, for example, head-up display (HUD) panelsin automotive and aircraft applications.

Turning now to FIGS. 1 through 8 b, several embodiments of wedge-shapedor tapered interlayers according to the present invention are provided.FIG. 1 is a cross-sectional view of an exemplary tapered interlayer thatincludes a tapered zone of varying thickness. As shown in FIG. 1, thetapered interlayer includes opposite first and second outer terminaledges. In the embodiment depicted in FIG. 1, the first and secondboundaries of the tapered zone are spaced inwardly from the first andsecond outer terminal edges of the interlayer. In such embodiments, onlya portion of the interlayer is tapered. In an alternative embodiment,discussed below, the entire interlayer is tapered. When the entireinterlayer is tapered, the tapered zone width is equal to the interlayerwidth and the first and second boundaries of the tapered zone arelocated at the first and second terminal edges, respectively.

As illustrated in FIG. 1, the tapered zone of the interlayer has a wedgeangle (θ), which is defined as the angle formed between a firstreference line extending through two points of the interlayer where thefirst and second tapered zone boundaries intersect a first (upper)surface of the interlayer and a second reference line extending throughtwo points where the first and second tapered zone boundaries intersecta second (lower) surface of the interlayer. When the first and secondsurfaces of the tapered zone are each planar, the wedge angle of thetapered zone is simply the angle between the first (upper) and second(lower) surfaces. However, as discussed in further detail below, incertain embodiments, the tapered zone can include at least one variableangle zone having a curved thickness profile and a continuously varyingwedge angle. Further, in certain embodiments, the tapered zone caninclude two or more constant angle zones, where the constant angle zoneseach have a linear thickness profile, but at least two of the constantangle zones have different wedge angles.

FIGS. 2-7 illustrate various tapered interlayers configured accordingembodiments of the present invention. FIG. 2 depicts an interlayer 20that includes a tapered zone 22 extending entirely from a first terminaledge 24 a of the interlayer 20 to a second terminal edge 24 b of theinterlayer 20. FIG. 3 illustrates an interlayer 30 that includes atapered zone 32 and a flat edge zone 33. The interlayer 30 depicted inFIG. 3 has a constant wedge angle θ_(c) that is greater than the overallwedge angle of the entire tapered zone 32. FIG. 4 illustrates aninterlayer 40 that includes a tapered zone 42 located between first andsecond flat edge zones 43 a,b. The interlayer 40 depicted in FIG. 4 hasa constant wedge angle θ_(c) that is greater than the overall wedgeangle of the entire tapered zone 42. FIG. 5 illustrates an interlayer 50that includes a tapered zone 52 located between first and second flatedge zones 53 a,b. FIG. 6 illustrates an interlayer 60 that does notinclude any flat end portions. Rather, the tapered zone 62 of theinterlayer 60 forms the entire interlayer 60. FIG. 7 illustrates aninterlayer 70 that includes a tapered zone 72 located between first andsecond flat edge zones 73 a,b.

As discussed above, the tapered interlayer can include one or moreconstant angle tapered zones, each having a width that is less than theoverall width of the entire tapered zone. Each tapered zone can have awedge angle that is the same as or different than the overall wedgeangle of the entire tapered zone. For example, the tapered zone caninclude one, two, three, four, five or more constant angle taperedzones. When multiple constant angle tapered zones are employed, theconstant angle tapered zones can be separated from one another byvariable angle tapered zones that serve to transition between adjacentconstant angle tapered zones.

In some embodiments, in addition to the interlayer(s), the multiplelayer panels may also include an interlayer(s) and, at least one polymerfilm, where the polymer film(s) may be between two layers of interlayer,such as encapsulated between two layers of interlayer. The use of apolymer film in multiple layer panels as described herein may enhancethe optical character or properties of the final panel, while alsoproviding other performance improvements, such as infrared absorption.Polymer films differ from polymer layers or interlayers in that thefilms alone do not provide the necessary penetration resistance andglass retention properties. The polymer film is also generally thinnerthan the sheet, and may generally have a thickness in the range of from0.001 to 0.25 mm. Poly(ethylene terephthalate) (“PET”) is one example ofa material used to form the polymer film. Examples of suitableconstructs where a polymer film may be used include(glass)//(interlayer)//(film)//(interlayer)//(glass) and(glass)//(interlayer)//(film)//(multiple layer interlayer)//(glass),where the polymer film may have coatings or any other functionallayer(s), as previously described.

According to some embodiments, multiple layer panels of the presentinvention may exhibit desirable acoustic properties, as indicated by,for example, the reduction in the transmission of sound as it passesthrough (i.e., the sound transmission loss of) the interlayer. In someembodiments, multiple layer panels of the present invention may exhibita sound transmission loss at the coincident frequency, measuredaccording to ASTM E90 at 20° C. and having panel dimensions of 50 cm by80 cm, of at least about 34, at least about 34.5, at least about 35, atleast about 35.5, at least about 36, at least about 36.5, at least about37, at least about 37.5, at least about 38, at least about 38.5, atleast about 39, at least about 39.5, at least about 40, or at leastabout 41. Such acoustic properties may be achieved even when, forexample, the combined thickness of the glass is less than 3.7 mm orthinner, as described in detail previously.

In some embodiments, asymmetric multiple layer panels as describedherein may exhibit a sound transmission loss at the coincident frequencythat is at least 2, at least about 2.5, at least about 3, at least about3.5, at least about 4, at least about 4.5, or at least about 5 dBgreater than the sound transmission loss at the coincident frequency ofa comparative symmetric panel. As used herein, the term “comparativesymmetric panel,” refers to a multiple layer panel formed from twosheets of clear glass and a single layer conventional interlayerdisposed therebetween. The conventional interlayer is formed frompoly(vinyl butyral) having a residual hydroxyl content of 18.5 weightpercent and a residual acetate content of less than 2 weight percent andincludes 38 phr of 3GEH plasticizer. The two sheets of glass have thesame combined thickness as a given asymmetric panel, but are of equalthickness, such that the symmetry of the two glass sheets in thecomparative panel is 1.0.

Additionally, or in the alternative, multiple layer panels of thepresent invention can have a suitable strength. For example, in someembodiments, multiple layer panels of the present invention can have adeflection stiffness of at least about 15, at least about 20, at leastabout 25, at least about 30, at least about 35, at least about 40, atleast about 45, at least about 50, at least about 55, at least about 60,at least about 70, or at least about 80 N/mm, measured as describedbelow in Example 2 below.

Multiple layer panels of the present invention may have excellentoptical properties, such as low haze and good clarity. Multiple layerpanels of the present invention may also have high visual transmittance(% T_(vis)) depending on the desired end use.

Multiple layer panels as described herein may be formed by any suitablemethod. The typical glass lamination process comprises the followingsteps: (1) assembly of the two substrates and the interlayer; (2)heating the assembly via an IR radiant or convective device for a first,short period of time; (3) passing the assembly into a pressure nip rollfor the first de-airing; (4) heating the assembly for a short period oftime to about 60° C. to about 120° C. to give the assembly enoughtemporary adhesion to seal the edge of the interlayer; (5) passing theassembly into a second pressure nip roll to further seal the edge of theinterlayer and allow further handling; and (6) autoclaving the assemblyat temperature between 135° C. and 150° C. and pressures between 150psig and 200 psig for about 30 to 90 minutes. Other methods forde-airing the interlayer-glass interface, as described according to oneembodiment in steps (2) through (5) above include vacuum bag and vacuumring processes, and both may also be used to form interlayers of thepresent invention as described herein.

The multiple layer panels of the present invention can be used for avariety of end use applications, including, for example, for automotivewindshields and windows, aircraft windshields and windows, panels forvarious transportation applications such as marine applications, railapplications, etc., structural architectural panels such as windows,doors, stairs, walkways, balustrades, decorative architectural panels,weather-resistant panels, such as hurricane glass or tornado glass,ballistic panels, and other similar applications.

The following examples are intended to be illustrative of the presentinvention in order to teach one of ordinary skill in the art to make anduse various embodiments of the invention and are not intended to limitthe scope of the invention in any way.

EXAMPLES Example 1

Several polymer sheets were formed by melt blending a poly(vinylbutyral) resin having a residual hydroxyl content of 18.5 weight percentand a residual acetate content of less than 2 weight percent (“Resin B”)with 38 parts per hundred resin (phr) of triethylene glycoldi-(2-ethylhexanoate) (“3GEH”) plasticizer. The resulting plasticizedresin was extruded to form a polymer sheet having a thickness of 0.76mm, which was then cut into several single-layer interlayer sheets eachhaving a glass transition temperature of 30° C. Interlayers having thisconstruction are referred to as interlayer “PVB-1” or a “conventionalmonolithic interlayer” herein.

Several three-layer (or tri-layer) interlayers were also formed bycoextruding Resin B with another poly(vinyl butyral) resin having aresidual hydroxyl content of 10.5 weight percent and a residual acetatecontent of less than 2 weight percent (“Resin A”) that had been meltblended with 75 phr of 3GEH. The resulting multiple layer interlayersincluded two outer layers formed from plasticized Resin B sandwiching aninner layer formed from plasticized Resin A, and they are referred to asinterlayer “PVB-2” herein.

Several multiple layer panels were then formed using PVB-1 and PVB-2,the single- and multiple-layer interlayers described above. Each panelwas formed by laminating an interlayer between a pair of 500 mm by 800mm sheets of glass having varying thicknesses. The lamination wasperformed by assembling the two glass substrates and interlayer with theinterlayer between the glass substrates; (2) heating the assembly toabout 40° C.; (3) passing the assembly into a pressure nip roll for thefirst deairing; (4) heating the assembly a second time to about 100° C.to give the assembly enough temporary adhesion to seal the edge of theinterlayer; (5) passing the assembly into a second pressure nip roll tofurther seal the edge of the interlayer and allow further handling; and(6) autoclaving the assembly at a temperature of about 143° C. andpressure of about 190 psig for about 30 minutes. The configurations ofeach of the panels are summarized in Table 1, below.

TABLE 1 Configurations of Panels Combined Glass Glass GlassConfiguration Thickness Panel Interlayer (mm/mm) (mm) Symmetry LG-1PVB-1 1.85/1.85 3.7 1 LG-2 PVB-1 2.1/1.6 3.7 0.76 LG-3 PVB-1 3.0/0.7 3.70.23 LG-4 PVB-1 1.6/1.6 3.2 1 LG-5 PVB-1  1.9/1.25 3.2 0.66 LG-6 PVB-21.85/1.85 3.7 1 LG-7 PVB-2 2.1/1.6 3.7 0.76 LG-8 PVB-2 3.0/0.7 3.7 0.23LG-9 PVB-2 1.6/1.6 3.2 1 LG-10 PVB-2  1.9/1.25 3.2 0.66

The sound transmission loss of each of the panels LG-1 through LG-10 wasdetermined according to the procedure described by ASTM E90 at 20° C.,for various frequencies over a range of 200 Hz to 8,000 Hz. The resultsare summarized in Table 2, below.

TABLE 2 Sound Transmission Loss of Glass Panels Sound Transmission Loss(dB) Sound Transmission Loss (dB) Panels with PVB-1 Interlayer Panelswith PVB-2 Interlayer Frequency LG-1 LG-2 LG-3 LG-4 LG-5 LG-6 LG-7 LG-8LG-9 LG-10 (Hz) 1.85/1.85 2.1/1.6 3.0/0.7 1.6/1.6 1.9/1.25 1.85/1.852.1/1.6 3.0/0.7 1.6/1.6 1.9/1.25 200 20.9 21.5 19.3 18.6 20.0 20.1 20.720.3 20.2 20.6 250 23.3 23.1 23.3 21.3 20.8 24.8 24.8 24.8 22.0 21.1 31526.5 26.4 26.3 24.1 23.2 25.8 25.6 25.9 23.4 22.9 400 28.0 28.0 28.126.9 26.0 28.6 28.9 28.1 26.4 25.4 500 28.8 29.0 28.6 27.3 27.1 30.530.3 30.3 28.3 27.5 630 31.2 31.0 30.4 30.5 30.2 31.6 31.7 31.3 30.930.7 800 32.4 32.4 31.9 31.3 31.1 33.4 33.3 33.0 32.1 32.2 1000 33.333.5 33.3 33.2 33.1 34.7 34.5 34.1 33.8 33.7 1250 35.0 35.1 35.0 34.434.3 36.7 36.4 35.8 35.2 35.1 1600 35.8 35.7 35.7 35.3 35.2 37.5 37.537.2 36.7 36.5 2000 35.3 35.2 35.1 35.8 35.7 38.4 38.3 37.7 37.7 37.62500 34.3 34.3 33.9 35.2 35.0 39.8 39.6 38.6 38.5 38.3 3150 32.0 31.830.6 33.0 32.5 40.3 40.1 37.7 39.5 39.2 4000 31.8 31.7 31.1 30.3 30.139.7 39.5 34.5 39.7 39.2 5000 36.2 36.2 36.4 32.6 32.1 38.4 38.1 34.139.4 38.5 6300 41.2 41.4 41.3 37.4 37.3 38.4 38.1 40.6 38.9 37.1 800043.5 43.7 44.3 40.0 40.1 42.4 42.6 43.7 39.4 38.6

Tables 3a and 3b, below, respectively summarize the sound transmissionloss at the coincident frequency for each of panels LG-1 through LG-5,which were formed with the conventional monolithic interlayers (PVB-1),and each of Panels LG-6 thorough LG-10, which were formed withmultilayer (trilayer) interlayers (PVB-2). Tables 3a and 3b alsosummarize the difference between the sound transmission loss at thecoincident frequency for each of panels LG-2 through LG-5 and LG-7through LG-10, and the sound transmission loss at the coincidentfrequency for a symmetrically configured panel utilizing a similarmonolithic or tri-layer interlayer and having a combined glass thicknessof 3.7 mm (e.g., LG-1 and LG-6, respectively).

TABLE 3a Sound Transmission Loss at the Coincident Frequency -Monolithic Interlayers Transmission Combined Loss at Glass GlassCoincident Coincident Decrease Glass Configuration Thickness FrequencyFrequency in TL from Panel Interlayer (mm/mm) (mm) Symmetry (Hz) (dB)LG-1 (dB) LG-1 PVB-1 1.85/1.85 3.7 1 4000 31.9 — LG-2 PVB-1 2.1/1.6 3.70.76 4000 31.8 −0.1 LG-3 PVB-1 3.0/0.7 3.7 0.23 3150 30.6 −1.3 LG-4PVB-1 1.6/1.6 3.2 1 4000 30.3 −1.6 LG-5 PVB-1  1.9/1.25 3.2 0.66 400030.1 −1.8

TABLE 3b Sound Transmission Loss at the Coincident Frequency - TrilayerInterlayers Combined Transmission Glass Glass Coincident Loss atDecrease Glass Configuration Thickness Frequency Coincident in TL fromPanel Interlayer (mm/mm) (mm) Symmetry (Hz) Frequency (dB) LG-6 (dB)LG-6 PVB-2 1.85/1.85 3.7 1 5000-6300 38.4 — LG-7 PVB-2 2.1/1.6 3.7 0.765000-6300 38.1 −0.3 LG-8 PVB-2 3.0/0.7 3.7 0.23 5000 34.1 −4.3 LG-9PVB-2 1.6/1.6 3.2 1 6300 38.9 0.5 LG-10 PVB-2  1.9/1.25 3.2 0.66 630037.1 −1.3

As shown in Tables 2 and 3a, above, none of the panels including PVB-1,a conventional monolithic interlayer (LG-1 through LG-5) achieve a soundtransmission loss (STL) greater than 32 dB at the coincident frequencyregion. Panel LG-1, which has a symmetric configuration and a combinedglass thickness of 3.7 mm, exhibits the best performance at thecoincident frequency. However, as shown by comparing the results forpanels LG-1 through LG-3 in Tables 2 and 3a, above, varying thethicknesses of the individual glass sheets in panels formed from PVB-1while maintaining the combined glass thickness of 3.7 mm results inrelatively minor differences in changes in the sound transmission loss.Similar trends can be observed at lower combined thicknesses as well, asshown by, for example, panels LG-4 and LG-5, which each have a combinedglass thickness of 3.2 mm with symmetries of 1 and 0.66 respectively.

In contrast, as shown in Tables 2 and 3b, varying the thickness of theindividual glass sheets in panels formed from tri-layer interlayers(PVB-2) while maintaining the same combined glass thickness results in amore pronounced change in sound transmission loss at the coincidentfrequency. For example, as shown by a comparison of panel LG-6 withpanels LG-7 and LG-8, a graphical representation of which is provided inFIG. 9, less symmetric glass configurations (i.e., symmetry of lessthan 1) result in lower sound transmission loss at the coincidentfrequency. As shown in Table 3b and in FIG. 9, the minimum symmetry atwhich the panels formed from a tri-layer interlayer exhibit a soundtransmission loss at the coincident frequency of at least 34 dB is 0.23.It is expected that the sound transmission loss at the coincidentfrequency for similar panels having symmetries less than 0.23 will beless than 34 dB, which is generally not suitable for use in applicationsrequiring acoustic performance.

Example 2

Two monolithic interlayers, PVB-1 and PVB-4, were used to constructmultiple layer panels. Interlayer PVB-1 was formed by melt blending 38phr of 3GEH plasticizer with a poly(vinyl butyral) resin having aresidual hydroxyl content of 18.5 weight percent, a residual acetatecontent of less than 2 weight percent, and a glass transitiontemperature of 30° C., as described in Example 1, as a flat polymersheet having an average thickness of 30 mils. Another conventionalmonolithic interlayer (“PVB-4”) was also formed by melt blending thesame poly(vinyl butyral) resin with 38 phr of 3GEH plasticizer andextruding the resulting plasticized resin to form a wedge shapedinterlayer having a wedge angle of 0.43 mrad and a glass transitiontemperature of 30° C.

Two multiple layer interlayers, PVB-2 and PVB-3, were also formed byco-extruding two different poly(vinyl butyral) resins into a tri-layerformation that included two stiff outer layers having similarcompositions, which were adjacent to and in contact with a softer innerlayer of a different composition. Interlayer PVB-2 was prepared andconfigured as described in Example 1, above, and interlayer PVB-3 wasconfigured in a similar manner except that the outer layers were formedfrom a poly(vinyl butyral) resin having a residual hydroxyl content of22 weight percent and a residual acetate content of less than 2 weightpercent (“Resin D”) and 27 phr of 3GEH plasticizer, and the inner layerwas formed from a poly(vinyl butyral) resin having a residual hydroxylcontent of 9 weight percent and a residual acetate content of less than2 weight percent (“Resin C”) plasticized with 70 phr of 3GEH. The outerlayers of interlayer PVB-2 had a glass transition temperature of 30° C.,while the outer layers of the interlayer PVB-3 had a glass transitiontemperature of 42° C. The glass transition temperature of the innerlayers of interlayers PVB-2 and PVB-3 was −2° C. Both PVB-2 and PVB-3had average thicknesses of 33 mils, with an average inner layerthickness of 4.5 mils.

Another tri-layer interlayer, PVB-5, was prepared and configured in thesame manner as PVB-2 except that PVB-5 was a wedge shaped interlayerhaving a wedge angle of 0.43 mrad. Interlayer PVB-5 had an inner layerthickness of 4.5 mils and interlayer thickness of 31 mils at the thinnerend. Interlayer PVB-6 was a wedge shaped interlayer having a wedge angleof 0.43 mrad and an interlayer thickness of 53 mils at the thinner end,and was prepared by combining interlayers PVB-3 and PVB-4 to form oneinterlayer. Alternatively, if desired, PVB-6 interlayer could be formedby using a co-extrusion process with plasticized Resin D and Resin C ina similar manner as used to form PVB-3 except with PVB-6 having a wedgeshape. The specific configurations of each of the PVB-1 through PVB-6interlayers are summarized in Table 4, below.

TABLE 4 Properties of PVB Interlayers Skin Core Residual ResidualInterlayer Hydroxyl Plasticizer Hydroxyl Plasticizer Core InterlayerPlasticizer Wedge Content Content T_(g) Content Content T_(g) ThicknessThickness Content Angle Interlayer (wt %) (phr) (° C.) (wt %) (phr) (°C.) (mils) (mils) (phr) (mrad) PVB-1 18.5 38 30 — — — — 30 38 0 PVB-218.5 38 30 10.5 75 −2 4.5 33 41 0 PVB-3 22 27 42 9  70 −2 4.5 33 31.5 0PVB-4 18.5 38 30 — — — — 30 38 0.43 PVB-5 18.5 38 30 10.5 75 −2 4.5 3141 0.43 PVB-6 — — — — — — — — — 0.43

Several multiple layer panels were formed by laminating samples of thePVB-1 through PVB-6 interlayers described above between pairs of 500 mmby 800 mm sheets of clear glass of varying thicknesses. Theconfigurations of each of the resulting panels (LG-11 through LG-39) aresummarized in Table 5, below. The sound transmission loss at thecoincident frequency was determined for each of panels LG-11 throughLG-37 according to ASTM E90 at 20° C., and the results are also providedin Table 5, below.

TABLE 5 Sound Transmission Loss at Coincident Frequency for Glass PanelsTransmission Thickness Thickness Loss at of Glass of Glass CombinedCoincident Coincident Glass Sheet 1 Sheet 2 Thickness FrequencyFrequency Panel Interlayer (mm) (mm) (mm) Symmetry (Hz) (dB) LG-11 PVB-12.1 2.1 4.2 1 3150 31.3 LG-12 PVB-1 1.85 1.85 3.7 1 4000 31.9 LG-13PVB-1 1.6 1.6 3.2 1 4000 30.3 LG-14 PVB-1 2.1 1.6 3.7 0.76 4000 31.8LG-15 PVB-1 1.9 1.25 3.15 0.66 4000 30.1 LG-16 PVB-1 1.6 0.7 2.3 0.445000 28.8 LG-17 PVB-1 2.1 0.7 2.8 0.33 4000 29.0 LG-18 PVB-1 2.3 0.7 3.00.30 4000 29.6 LG-19 PVB-1 3 0.7 3.7 0.23 3150 30.6 LG-20 PVB-2 2.1 2.14.2 1 5000 38.2 LG-21 PVB-2 1.85 1.85 3.7 1 5000-6300 38.4 LG-22 PVB-21.6 1.6 3.2 1 6300 38.9 LG-23 PVB-2 2.1 1.6 3.7 0.76 5000-6300 38.1LG-24 PVB-2 1.9 1.25 3.15 0.66 6300 37.1 LG-25 PVB-2 1.6 0.7 2.3 0.448000 36.7 LG-26 PVB-2 2.1 0.7 2.8 0.33 6300 35.6 LG-27 PVB-2 2.3 0.7 3.00.30 6300 35.6 LG-28 PVB-2 3 0.7 3.7 0.23 5000 34.1 LG-29 PVB-3 2.1 2.14.2 1 5000 39.3 LG-30 PVB-3 1.85 1.85 3.7 1 — — LG-31 PVB-3 1.6 1.6 3.21 6300 39.4 LG-32 PVB-3 2.1 1.6 3.7 0.76 5000-6300 38.5 LG-33 PVB-3 1.91.25 3.15 0.66 — — LG-34 PVB-3 1.6 0.7 2.3 0.44 8000 37.4 LG-35 PVB-32.1 0.7 2.8 0.33 5000 36.5 LG-36 PVB-3 2.3 0.7 3.0 0.30 5000 35.6 LG-37PVB-3 3 0.7 3.7 0.23 5000 34.5 LG-38 PVB-5 1.6 0.7 2.3 0.44 — — LG-39PVB-6 1.6 0.7 2.3 0.44 — —

As shown in Table 5, above, there is no clear trend in soundtransmission loss for panels LG-11 through LG-19, which utilize thesingle-layer, non-acoustic PVB-1 interlayer. Panels utilizing theacoustic interlayers, PVB-2 and PVB-3, tend to exhibit decreasing soundtransmission loss with glass configurations of reduced symmetry. Thesound transmission loss at the coincident frequency as a function ofsymmetry for panels LG-29 through LG-37, which contain interlayer PVB-3,is also summarized graphically in FIG. 12. As shown in Table 5, above,at a symmetry of 0.23, the sound transmission losses exhibited by panelsLG-28 and LG-37 were greater than 34 dB, which is higher thansymmetrically configured, non-acoustic panels LG-1 through LG-3.However, further reducing the symmetry of panels formed from PVB-3 (atri-layer acoustic interlayer) will reduce the sound transmission lossto a value near the sound transmission loss values of panels formed fromnon-acoustic PVB layers.

As shown by a comparison of LG-11 through LG-13, LG-20 through LG-22,and LG-29 through LG-31, the sound transmission loss at the coincidentfrequency of the panels appears to be independent of glass thickness.For example, each of LG-11 through LG-13, LG-20 through LG-22, and LG-29through LG-31 have a symmetry of 1, but have combined glass thicknessesof 4.2 mm (LG-11, LG-20, and LG-29), 3.7 mm (LG-12, LG-21, and LG-30),and 3.2 mm (LG-12, LG-22, and LG-31). Despite the differences incombined glass thickness, each of the groups LG-11 through LG-13, LG-20through LG-22, and LG-29 through LG-31 exhibit a similar soundtransmission loss at the coincident frequency. Thus, adjusting thecombined glass thickness alone does not appear to sufficiently alter thesound transmission loss of the panels.

The deflection stiffness of several of the panels was also tested usingthe three-point bending test. A diagram of the apparatus used to conductthe three-point bending test is provided in FIG. 10. After beingconditioned at a constant humidity of 50% and a temperature of 23° C.for two hours, the test panel was loaded into the apparatus as shown inFIG. 10. Two fixed supports with a span of 15 cm were applied to theunderside of the panel, and a third point, a cylindrical rod with adiameter of 0.953 cm and a length of 5.08 cm, was applied at the upperside of the panel, near its center. A force was then applied at thethird point to create a constant velocity of about 1.27 mm/min on thetest panel. Values for the load on the test panel (in N) and thedeflection of the panel (in cm) were recorded. The values were plottedagainst one another, in a manner similar to the exemplary graph providedin FIG. 11, and the deflection stiffness of the panel was calculated bydetermining the average slope of the line created by graphing the loadversus deflection of the panel prior to the apparent drop in the load,which generally signifies breakage of the panel. The results for thepanels tested are summarized in Table 6, below.

TABLE 6 Deflection Stiffness Glass Panels Transmission Combined Loss atGlass Glass Deflection Coincident Coincident Glass ConfigurationThickness Stiffness Frequency Frequency Panel Interlayer (mm/mm) (mm)(N/mm) (Hz) (dB) LG-13 PVB-1 1.6/1.6 3.2 26 4000 30.3 LG-14 PVB-12.1/1.6 3.7 38 4000 31.8 LG-11 PVB-1 2.1/2.1 4.2 54 3150 31.3 LG-22PVB-2 1.6/1.6 3.2 21 6300 38.9 LG-23 PVB-2 2.1/1.6 3.7 31 5000-6300 38.1LG-20 PVB-2 2.1/2.1 4.2 48 5000 38.2 LG-31 PVB-3 1.6/1.6 3.2 30 630039.4 LG-32 PVB-3 2.1/1.6 3.7 47 5000-6300 38.5 LG-29 PVB-3 2.1/2.1 4.258 5000 39.3

As shown in Table 6, above, panels comprising PVB-3, which includesstiffer outer layers, exhibit higher deflection stiffness than panelsformed from the PVB-2 or PVB-1 interlayers. Additionally, panels formedfrom the PVB-3 interlayer also exhibit a higher sound transmission lossat the coincident frequency for all glass configurations as shown inTable 6, above. Accordingly, as shown by, for example, a comparison ofLG-31 and LG-23, panels utilizing the PVB-3 interlayer can utilize alower combined glass thickness (3.2 mm for LG-31 as compared to 3.7 mmfor LG-23), while still providing higher sound transmission loss (39.4dB for LG-31 as compared to 38.1 dB for LG-23) and exhibiting similardeflection stiffness (30 N/cm for LG-31 as compared to 31 N/cm forLG-23).

While the invention has been disclosed in conjunction with a descriptionof certain embodiments, including those that are currently believed tobe the preferred embodiments, the detailed description is intended to beillustrative and should not be understood to limit the scope of thepresent disclosure. As would be understood by one of ordinary skill inthe art, embodiments other than those described in detail herein areencompassed by the present invention. Modifications and variations ofthe described embodiments may be made without departing from the spiritand scope of the invention.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present disclosurecan be used interchangeably with any ranges, values or characteristicsgiven for any of the other components of the disclosure, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. For example, an interlayer canbe formed comprising poly(vinyl butyral) having a residual hydroxylcontent in any of the ranges given in addition to comprising aplasticizers in any of the ranges given to form many permutations thatare within the scope of the present disclosure, but that would becumbersome to list. Further, ranges provided for a genus or a category,such as phthalates or benzoates, can also be applied to species withinthe genus or members of the category, such as dioctyl terephthalate,unless otherwise noted.

The invention claimed is:
 1. A multiple layer panel comprising: a firstsubstrate having a first nominal thickness; a second substrate having asecond nominal thickness, wherein said second nominal thickness is atleast 0.5 mm less than said first nominal thickness and wherein saidsecond nominal thickness is at least 1.1 mm; and a multiple layeracoustic interlayer disposed between and in contact with each of saidfirst and said second substrates, wherein said multiple layer interlayercomprises— a first polymer layer comprising a first poly(vinyl acetal)resin and at least one plasticizer; and a second polymer layer adjacentto and in contact with said first polymer layer, wherein said secondpolymer layer comprises a second poly(vinyl acetal) resin and at leastone plasticizer, wherein said first and said second poly(vinyl acetal)resins have respective first and second residual hydroxyl contents, andwherein said second residual hydroxyl content is at least 2 weightpercent different than said first residual hydroxyl content, and whereinsaid interlayer has at least one polymer layer having a glass transitiontemperature of 25° C. or less, wherein the ratio of said second nominalthickness to said first nominal thickness is in the range of from atleast 0.23:1 to less than 1:1, and wherein the sum of said first andsaid second nominal thicknesses is less than 3.7 mm.
 2. The multiplelayer panel of claim 1, wherein said second nominal thickness is lessthan 1.8 mm.
 3. The multiple layer panel of claim 1, wherein said ratioof said second nominal thickness to said first nominal thickness is lessthan 0.75:1.
 4. The multiple layer panel of claim 1, wherein said firstnominal thickness is in the range of from 1.6 mm to 2.9 mm, wherein saidsecond nominal thickness is in the range of from 1.2 mm to 1.8 mm, andwherein the sum of said first and said second nominal thicknesses is atleast 3.0 mm.
 5. The multiple layer panel of claim 1, wherein saidmultiple layer panel exhibits a sound transmission loss at thecoincident frequency, measured according to ASTM E90, of at least 34 dB.6. The multiple layer panel of claim 1, wherein said interlayer includesat least one tapered zone and wherein the tapered zone has a minimumwedge angle of at least 0.10 mrad.
 7. A multiple layer panel comprising:a first substrate having a first nominal thickness; a second substratehaving a second nominal thickness, wherein said second nominal thicknessis at least 0.5 mm less than said first nominal thickness, and whereinsaid second nominal thickness is at least 1.1 mm and less than 1.8 mm;and an acoustic interlayer disposed between and in contact with each ofsaid first and said second substrates, wherein said interlayer comprisesa first polymer layer comprising a first poly(vinyl acetal) resin and atleast one plasticizer, wherein the ratio of said second nominalthickness to said first nominal thickness is in the range of from atleast 0.23:1 to less than 1:1, wherein the sum of said first and saidsecond nominal thicknesses is less than 3.7 mm and wherein said multiplelayer panel exhibits a sound transmission loss at the coincidentfrequency, measured according to ASTM E90, of at least 34 dB.
 8. Themultiple layer panel of claim 7, wherein the ratio of said secondnominal thickness to said first nominal thickness is not more than0.75:1.
 9. The multiple layer panel of claim 7, wherein said interlayerfurther comprises a second polymer layer adjacent to and in contact withsaid first polymer layer, wherein said second polymer layer comprises asecond poly(vinyl acetal) resin and at least one plasticizer, whereinsaid first and said second poly(vinyl acetal) resins have respectivefirst and second residual hydroxyl contents, and wherein said first andsaid second polymer layers have respective first and second glasstransition temperatures, and wherein at least one of the followingcriteria (i) through (iii) is true— (i) the difference between saidfirst residual hydroxyl content and said second residual hydroxylcontent is at least 2 weight percent; (ii) the difference between saidfirst glass transition temperature and said second glass transitiontemperature is at least 13° C.; and (iii) the difference between theplasticizer content of said first polymer layer and the plasticizercontent of said second polymer layer is at least 5 phr.
 10. The multiplelayer panel of claim 7, wherein said first nominal thickness is in therange of from 1.6 mm to 2.9 mm, wherein the second nominal thickness isat least 1.2 mm, and wherein the ratio of said second nominal thicknessto said first nominal thickness is not more than 0.60:1.
 11. Themultiple layer panel of claim 7, wherein said interlayer includes atleast one tapered zone and wherein the tapered zone has a minimum wedgeangle of at least 0.10 mrad.
 12. A multiple layer panel comprising: afirst substrate having a first nominal thickness; a second substratehaving a second nominal thickness, wherein said second nominal thicknessis at least 0.5 mm less than said first nominal thickness and whereinsaid second nominal thickness is at least 1.1 mm; and a multiple layeracoustic interlayer disposed between and in contact with each of saidfirst and said second substrates, wherein said multiple layer interlayercomprises— a first polymer layer comprising a first poly(vinyl acetal)resin and at least one plasticizer wherein said first polymer layer hasa first glass transition temperature; and a second polymer layeradjacent to and in contact with said first polymer layer, wherein saidsecond polymer layer comprises a second poly(vinyl acetal) resin and atleast one plasticizer wherein said first polymer layer has a first glasstransition temperature, wherein said first and said second poly(vinylacetal) resins have respective first and second residual hydroxylcontents, and wherein said second residual hydroxyl content is at least2 weight percent different than said first residual hydroxyl content,wherein the difference between said first glass transition temperatureand said second glass transition temperature is at least 13° C.; andwherein the difference between the plasticizer content of said firstpolymer layer and the plasticizer content of said second polymer layeris at least 5 phr, wherein the ratio of said second nominal thickness tosaid first nominal thickness is in the range of from at least 0.23:1 toless than 1:1, and wherein the sum of said first and said second nominalthicknesses is less than 3.7 mm.
 13. The multiple layer panel of claim12, wherein said multiple layer panel exhibits a sound transmission lossat the coincident frequency, measured according to ASTM E90, of at least34 dB.
 14. The multiple layer panel of claim 12, wherein said firstnominal thickness is in the range of from 1.6 mm to 2.9 mm, wherein thesecond nominal thickness is at least 1.2 mm, and wherein the ratio ofsaid second nominal thickness to said first nominal thickness is notmore than 0.60:1.